Crews were also called to reports of a car in floodwater at Rooty Hill, which turned out to be an abandoned vehicle.

Endeavour Energy said power had been restored to about 43,000 properties by Thursday evening, with 780 still in the dark.

"In some cases, damage to the wiring within homes may prevent this as it would be unsafe for these premises to be reconnected," the company said in a statement.

Ausgrid said about 3500 customers lost power in the Berowra and Woy Woy districts.

Authorities reminded people to stay away from stormwater drains following last week's tragedy when an 11-year-old boy died after he was sucked into one while playing on a bodyboard in a park near Wollongong.

The state's northern rivers, mid north coast and Northern Tablelands regions were forecast to be hit by further storm activity on Thursday evening.